In the past few years considerable effort has gone into the design and development of so-called passive vehicle occupant restraint belt systems, i.e., restraint belt systems that automatically move to an occupant-restraining configuration when an occupant is seated in the vehicle and the vehicle door is closed and automatically transfer to an occupant-releasing configuration when the vehicle door is opened. Many such passive systems, and components therefor, have been proposed in anticipation that the Government will require that they be incorporated in new vehicles and that purchasers of new vehicles will want them in any event. Many of the systems that have been advanced thus far and, no doubt, many that will be proposed in the future have a belt transfer member that engages a portion of the restraint belt or in some cases a control belt and is driven along a guide rail by a drive system between a release position and a restraint position. The drive wire that transmits the output of an electric motor or a mechanical motion amplifier to the movable belt transfer member is a very important component of many passive restraint systems, inasmuch as it is called upon to position the belt transfer member at the release and restraint positions with a relatively high degree of precision over many thousands of cycles of operation. Accordingly, it must be constructed to fairly close tolerances out of durable materials and must be capable of moving along curved paths, which means that it must be somewhat flexible. At the same time it must have sufficient stiffness to transmit motion by pushing the belt transfer member along the guide rail.
A very adequate form of transfer wire for passive belt systems is the so-called racked wire. Racked wires consist of a continuous core wire element and a continuous tooth wire element wrapped helically around the core wire element and securely fixed thereto. A disadvantage of a racked wire for driving the movable belt transfer member is the fact that the portion which moves in and out of the guide rail is subject to abrasion and also subjects the guide rail to abrasion. Moreover, the rubbing between the wire and rail makes a fair amount of noise, which can be bothersome to the occupant. Possible solutions to the noise and abrasion problems are to encase the part of the drive wire that moves in and out of the guide rail in a plastic cover or sheet or to apply a plastic coating over it. Those solutions are not altogether satisfactory, however, because they increase the cross-sectional size of the drive wire and conflict with the objective of minimizing the size and weight of the rail.
FIG. 2 of the accompanying drawings shows another possible solution to the abrasion and noise problem that has been tried. The drive wire 30 comprises a wire core 12 which is fastened at one end to a slider 14 that moves along the guide rail and carries an emergency release buckle 16 to which the belt B is connected by a buckle tongue 18. The other end of the core wire 12 receives a cap 20. The portion 12a of the core wire 12 that moves in and out of the guide rail as the belt transfer member 14 moves between the restraint and release positions along the guide rail has a plastic covering 22. The remainder of the core wire 12 has the tooth wire 24. In order to minimize the diameter of the portion 12a of the drive wire the tooth wire has been removed. The prior solution illustrated in FIG. 2 has the disadvantage of being quite difficult and expensive to make. It is also difficult and expensive to manufacture special racked wires having tooth wire wound only over part of the length and to apply a cover or coating to only part of the total length of the drive wire.